1. Field of the Invention
This invention relates to self-adjusting pliers having jaws which pivot about a jaw portion first pivot point during a first phase and a jaw portion second pivot point during the second closing phase and, more specifically, to a pair of pliers which utilizes a cam during the transition between the first phase of operation and the second phase of operation.
2. Background Information
Pliers are used to grasp or otherwise act upon a workpiece. A pair of pliers includes two elongated members joined by a pivot pin at an intersection on the medial portion of the members. One end of each elongated member forms a jaw and the other end of the elongated members forms a handle. A workpiece located between the jaws may be grasped by an operator drawing the handle portions towards each other. Hand tools have also been constructed using two elongated members which do not intersect, but which are joined by a link member, see, e.g., U.S. Pat. No. 3,600,686. The link member forms a toggle joint with one of the handle portions. The toggle joint augments to force applied by the user as the angle of toggle joint approaches 180 degrees.
The basic pair of pliers was improved to be self-adjusting by incorporating a slot in one elongated member which allows the jaw portion of the other elongated member to be moved relative to the pivot point, see, e.g., U.S. Pat. No. 1,508,510. Further improvements to pliers allow the pliers to self-adjust to the size of the workpiece and further incorporate a two pivot system, see, e.g. U.S. Pat. No. 6,014,917. The two pivot system provides for a first pivot point that allows the jaw members to close until contacting a workpiece whereupon the pivot point shifts to the second pivot point, which is typically located closer to the workpiece, thereby giving the user greater leverage while drawing the handle portions towards each other. The second pivot point is typically created by a pawl which engages a toothed rack. During the initial phase of operation, the pawl is spaced apart from the rack, or allowed to slide over the rack. When the jaws of the pliers contact the workpiece, the pawl is shifted into engagement with the rack thereby creating the second pivot point.
The disadvantage of pliers which utilize a pawl to form the second pivot point is that such pliers are subject to a periodic force variation as the pawl engages the rack. That is, because the teeth on the rack are disposed at fixed incremental locations and because the pawl moves over the rack teeth, the pawl may not be positioned to engage a tooth on the rack at the point when the jaws of the pliers contact the workpiece. When this occurs, the pawl must move backwards on the rack to engage a tooth. The larger the tooth, the more variation there is between the point at which the jaws contact the workpiece and the point at which the second pivot is created. One method of reducing the variation is to utilize racks having smaller teeth. Smaller teeth, however, are weaker and may not be able to tolerate the stress placed on the tooth. Additionally, fine teeth are difficult to manufacture and are subject to degradation from repeated use.
Further, prior art pliers have not successfully combined the self-adjusting and force augmenting features with a locking feature. For example, a typical toggle joint tool utilizes an over-toggle pin to lock the tool. An over-toggle pin, however, requires that the toggle joint pass through the toggle position to engage. After the toggle joint passes through the toggle position, the closing force is reduced.
There is, therefore, a need for a pair of pliers that operate about a first pivot during a first pivot phase and about a second pivot during a second pivot phase and which does not utilize a pawl and tooth rack combination to create the second pivot.
There is a further need for a pair of pliers that operate about a first pivot and a second pivot which does not have a variation during the transition between the first pivot and the second pivot.
There is a further need for a pair of pliers that incorporates a self-adjusting mechanism, a force augmentation mechanism and a locking mechanism.
These needs, and others, are satisfied by the present invention which provides a pair of pliers having two opposed members, a first plier member assembly and a second plier member assembly which are joined at a jaw portion first pivot point. The pliers further include a jaw portion second pivot point, located closer to the jaws of the pliers than the first pivot point. The pliers further include a cam assembly and a tension assembly. The pliers member assemblies pivot about the first pivot point during a first pivot phase of operation. When the jaws of the pliers contact a workpiece, the pliers enter a transition phase wherein the cam assembly engages the tension assembly. After the tension assembly is engaged, the jaws pivot about the jaw portion second pivot point. That is, at the end of the transition phase the cam is fully engaged against the tension assembly thereby resisting further movement along the tension assembly. Because the first link is not free to rotate about the first pivot point, the jaws of the pliers rotate about the second pivot point.
The pliers include a rigid first plier member assembly having a jaw portion, an intermediate portion, and a handle portion. The first plier member assembly further includes a first link which is coupled at one end to the handle portion of the first plier member assembly and which has a distal end having an end plate upon which the cam assembly and a jaw portion second pivot pin are disposed. The first plier member assembly further includes a tension bar having an elongated member which extends between the second phase pivot pin and the rotating cam. The first plier member assembly handle portion includes a first link pivot point and a jaw portion first pivot point. The pliers also have a second plier member assembly which includes a movable member with a jaw portion and an intermediate portion, a handle member, and a second link. The second plier member assembly handle member is pivotally attached to the second plier member assembly moving member. The second plier member assembly moving member further includes an opening on the intermediate portion for the second phase pivot pin.
A second link is rotatedly coupled to the second plier member assembly handle member at a toggle pivot point and form a toggle joint. The second link is also rotatably coupled to the first plier member assembly handle portion at the jaw portion first pivot point. A first phase pivot pin couples the second link to the first plier member assembly handle portion. Thus, the second plier member assembly jaw portion is coupled to both the first link and the second link. Both the first link and the second link are coupled to the first plier member assembly handle portion. Thus, when the distance between the pivot points on the second plier member assembly movable member and the pivot points on the first plier member assembly handle portion are about the same, the four pivot points form a parallelogram In this configuration, the motion of the second plier member assembly jaw portion relative to the first plier member assembly jaw portion can be controlled so that the jaws move parallel to each other during the first phase (described below).
The second plier member assembly handle member also interacts with a cam in the cam assembly, holding the cam out of contact with the tension bar during the first phase rotation, and allowing the cam to engage the tension bar assembly during the intermediate phase and the second phase. A cam spring causes the cam to engage the tension bar.
The pliers operate in three phases. At the initial starting point, the plier jaw portions are separated and a workpiece is disposed therebetween. During the first pivot phase of operation the first plier member assembly and the second plier member assembly pivot about the jaw portion first phase pivot pin. When the jaw portions contact the workpiece, the pliers enter an intermediate phase wherein rotation about the first phase pivot pin ceases and rotation about the toggle pivot point begins. As the second plier member assembly handle member rotates relative to the second link, the second plier member assembly handle member releases the cam assembly causing the cam assembly to engage the tension bar assembly. When the cam assembly has engaged the tension bar assembly, rotation between the first link and the first plier member assembly handle portion ceases, thereby ending the transition phase and begins the second pivot phase. During the second pivot phase the second plier member assembly toggle joint is moved toward, or even through, the toggle position. As the second plier member assembly toggle joint moves toward the toggle position, the second plier member assembly movable member pivots about the jaw portion second phase pivot pin. The jaw portion second phase pivot pin is located substantially closer to the workpiece than the jaw portion first phase pivot pin. Because the transition phase relies on a cam assembly acting against a tension assembly, the pliers do not slip backwards as would a tool utilizing a pawl and tooth rack system.
Additionally, the nature of the toggle joint provides the force augmentation mechanism whereby the force applied by the user is enhanced. That is, during the second phase as the toggle angle approaches 180 degrees, the theoretical force approaches infinity. Due to frictional forces, infinite force is not reached, but the closing force is still higher than the force applied by the user.
The pliers may also have a mechanical locking assembly. The locking assembly is, preferably, disposed at the toggle joint. The locking assembly may be a pawl and toothed rack device having the pawl attached to one member of the toggle joint and the rack attached to the other member of the toggle joint. As the toggle joint opens, the pawl engages the rack. At the end of the second phase, the pawl has engaged the rack thereby locking the toggle joint in place.